1. Field of the Invention
The present invention relates generally to an apparatus for automatically detecting the movement of a moving object, and more particularly, to a microwave motion-detection apparatus employing a Gunn oscillator in a self-detecting mode.
2. Description of the Prior Art
Microwave detection systems utilizing the Doppler principle are commonly used to actuate sliding doors and detect intruders or the like. In Doppler-type systems, frequency differences between generated and reflected electrical signals are monitored to detect the movement of objects within a monitored area. In practice, such systems ae plagued by false alarms despite the introduction of filtering networks and the use of signal-isolation techniques. Furthermore, as filtering networks are added, the Doppler-type systems become extremely complex and, consequently, expensive to implement and maintain.
In one system a transmitter having a Gunn oscillator is employed to produce a microwave signal in the X-band region, between 10.500 and 10.550 gigahertz (GHz). A horn antenna transmits and directs the microwave signal to the area under observation. When an object moves within the area it causes an electrical signal to be reflected back toward the transmitter. The electrical signal has a frequency which is Doppler shifted from the transmitted signal by an amount corresponding to the movement of the object. A receiver having a diode detector is disposed proximate the transmitter to detect the reflected signal and to produce an indication of the presence of the moving object. Since a separate transmitter and receiver are required, such systems are relatively expensive to manufacture.
Furthermore, it should be noted that a Gunn oscillator requires a highly regulated DC potential difference across its input terminals in order to produce an output signal at a preselected frequency in the X-band region of the electromagnetic specturm. Should the potential difference exceed that specified by the manufacturers then the Gunn device may be permanently damaged and should it vary much from an optimum value then the frequency of the output signal will correspondingly vary. In this regard the Federal Communications Commission has allocated the frequency spectrum between 10.500 and 10.550GHz to microwave transmitters used as field disturbance sensors in the security industry. Consequently, microwave transmitters producing signals outside the allocated spectrum can not be utilized in commercially available field disturbance sensors. As a result the potential difference applied to commercial Gunn oscillators must be constant. In addition, the bias current flowing through each one of a family of Gunn oscillators may vary over a wide range of values, e.g., between 90 and 120 milliamps. Because of this wide variation in DC bias current had since reflected signals tend to cause the bias current to vary with time, Gunn oscillators have not been used as a receiver or detection device for reflected signals in a commercial security system.
In this regard, it should be noted that a Gunn oscillator has been used as a receiver in a laboratory experiment. In the experiment, a power supply having a variable output voltage was connected through a series resistance to the terminals of a Gunn oscillator and the voltage was adjusted to cause the oscillator to produce X-band radiation. Variations in bias current due to reflected signals are sensed as voltage variations across the series resistor. However, such an apparatus is not capable of automatically providing a constant potential difference when a different Gunn oscillator is employed or when the bias current varies due to temperature fluctuations or due to variation of the Gunn device characteristics with time.
Examples of prior art motion detection systems include U.S. Pat. No. 3,634,884, entitled "Motion Dection System", by Vernon B. Ross; U.S. Pat. No. 3,665,443, entitled "Ultrasonic Intrusion Alarm", by Aaron A. Galvin; U.S. Pat. No. 3,742,434, entitled "Automatic Door-Opening System Using An Acoustic Object Detection System", by Warren L. Leyde and Delbert E. Marker; and U.S. Pat. No. 3,813,669 entitled "Frequency Filter Circuit Apparatus", by Leonard Thomas Saunders.